The permanent alteration of the color of keratinous fibres, in particular human hair, by the application of hair dyes is well known. In order to provide the consumer with a permanent and intense hair color, a very complex chemical process is utilized. Permanent hair dyeing formulations typically comprise oxidative hair dye precursors, i.e., developers and couplers, which diffuse into the hair through the cuticle and into the cortex, where the precursors then react with an oxidising agent, such as hydrogen peroxide, and each other to form larger-sized dye molecules. More specifically, an oxidizing agent, such as hydrogen peroxide, activates a developer dye and the activated developer then reacts with a coupler dye to form a larger-sized dye molecule that imparts color to the hair. These larger-sized, resultant dye molecules provide permanent, wash-resistant color, because these dyes are too large to readily diffuse out of the hair during subsequent washing. Different combinations of developers and couplers produce different shades of hair color.
In order to achieve desirable shades in the red area, 1-hydroxyethyl-4,5-diaminopyrazole is used, by itself or in a mixture with other developer substances, in combination with suitable coupler substances. When 1-hydroxyethyl-4,5-diaminopyrazole is used with a standard oxidant system, i.e., ammonium hydroxide and hydrogen peroxide at pH 10, natural and fashionable red shades are achieved. However, there exists a need for additional dyeing compounds that can provide desirable red shades, particularly when used with other oxidant systems, i.e., ammonium carbonate, hydrogen peroxide, and, optionally, a radical scavenger at pH 9.0.